This invention relates to sewing machines and, more particularly, to electronically controlled sewing machines including an optically switch buttonhole mechanism.
U.S. Pat. No. 4,216,732 discloses a sewing machine having an optical buttonhole switching arrangement in which the movements of reflective areas carried on a movable buttonhole foot are sensed as the foot is moved by the fabric feeding movement of a feed dog against the garment being sewn. The foot includes adjustable optical targets whose movements are sensed by photosensors carried on the sewing head. The spacing of the optical targets may be manually adjusted to accommodate buttons of different sizes. The photosensors are connected to an electronic circuit whose output is used to control the retrieval of buttonhole stitching information from an electronic memory. While such an arrangement performs generally satisfactorily, it has been found that false triggering of the sensors by the operator when the sewing machine is stopped occasionally occurs. This false triggering occurs primarily after the machine comes to a stop and the operator inadvertently places a hand, fabric, scissors or the like, under the sewing head within the field of view of the photosensors.
It is therefore an object of the present invention to provide a method and arrangement to prevent such false triggering.